The invention relates to an aircraft tire. Aircraft tires are distinguished in particular by the combination of an inflation pressure greater than 9 bar and a relative deflection greater than 30%.
The deflection of a tire is defined by the radial deformation of the tire, or variation in the radial height, when it changes from a non-loaded state to a statically loaded state, under rated load and pressure conditions.
It is expressed in the form of a relative deflection, defined by the ratio of this variation in the radial height of the tire to half the difference between the external diameter of the tire and the maximum diameter of the rim measured on the hook. The external diameter of the tire is measured statically in a non-loaded state at the rated pressure.
The reinforcement armature or reinforcement of tires and in particular of aircraft tires is currently—and most frequently—constituted by stacking one or more plies conventionally referred to as “carcass plies”, “crown plies”, etc. This manner of designating the reinforcement armatures originates from the manufacturing process, which consists of producing a series of semi-finished products in the form of plies, provided with cord reinforcing threads which are frequently longitudinal, which are subsequently assembled or stacked in order to build a tire blank. The plies are produced flat, with large dimensions, and are subsequently cut according to the dimensions of a given product. The plies are also assembled, in a first phase, substantially flat. The blank thus produced is then shaped to adopt the toroidal profile typical of tires. The semi-finished products referred to as “finishing” products are then applied to the blank, in order to obtain a product ready to be vulcanized.
Such a type of “conventional” process involves, in particular for the phase of manufacture of the blank of the tire, the use of an anchoring element (generally a bead wire), used for anchoring or holding the carcass reinforcement in the zone of the beads of the tire. Thus, in this type of process, a portion of all the plies constituting the carcass reinforcement (or only a part thereof) is turned up around a bead wire arranged in the tire bead. In this manner, the carcass reinforcement is anchored in the bead.
The fact that this conventional type of process is becoming more widespread in the industry, despite numerous variants in the manner of producing the plies and assemblies, has led the person skilled in the art to use a vocabulary modeled on the process; hence the generally accepted terminology, comprising in particular the terms “plies”, “carcass”, “bead wire”, “shaping” to designate the change from a flat profile to a toroidal profile, etc.
There are nowadays tires which do not, properly speaking, comprise “plies” or “bead wires” in accordance with the preceding definitions. For example, document EP 0 582 196 describes tires manufactured without the aid of semi-finished products in the form of plies. For example, the reinforcement elements of the different reinforcement structures are applied directly to the adjacent layers of rubber mixes, the whole being applied in successive layers to a toroidal core the form of which makes it possible to obtain directly a profile similar to the final profile of the tire being manufactured. Thus, in this case, we no longer find “semi-finished products”, nor “plies”, nor “bead wires”. The base products, such as the rubber mixes and the reinforcement elements in the form of cords or filaments, are applied directly to the core. As this core is of toroidal form, the blank no longer has to be shaped in order to change from a flat profile to a profile in the form of a torus.
Furthermore, the tires described in this document do not have the “conventional” upturn of the carcass ply around a bead wire. This type of anchoring is replaced by an arrangement in which circumferential cords are arranged adjacent to said sidewall reinforcement structure, the whole being embedded in an anchoring or bonding rubber mix.
There are also processes for assembly on a toroidal core using semi-finished products specially adapted for quick, effective and simple laying on a central core. Finally, it is also possible to use a mixture comprising both certain semi-finished products to produce certain architectural aspects (such as plies, bead wires, etc.), whereas others are produced from the direct application of mixes and/or reinforcement elements.
In the present document, in order to take into account recent technological developments both in the field of manufacture and in the design of products, the conventional terms such as “plies”, “bead wires”, etc., are advantageously replaced by neutral terms or terms which are independent of the type of process used. Thus, the term “carcass-type reinforcing thread” or “sidewall reinforcing thread” is valid as a designation for the reinforcement elements of a carcass ply in the conventional process, and the corresponding reinforcement elements, generally applied at the level of the sidewalls, of a tire produced in accordance with a process without semi-finished products. The term “anchoring zone”, for its part, may equally well designate the “traditional” upturn of a carcass ply around a bead wire of a conventional process and the assembly formed by the circumferential reinforcement elements, the rubber mix and the adjacent sidewall reinforcement portions of a bottom zone produced with a process with application to a toroidal core.
In what follows, “linear density” is understood to mean the weight in grammes of one thousand meters of a reinforcing thread. The linear density is expressed in tex. The stress to which a reinforcing thread is subjected or the modulus of this reinforcing thread are expressed in “cN/tex”, cN meaning centinewton.
“Axial” is understood to mean a direction parallel to the axis of rotation of the tire; this direction may be “axially inner” when it is directed towards the inside of the tire and “axially outer” when it is directed towards the outside of the tire.
“Radial” is understood to mean a direction perpendicular to the axis of rotation of the tire and passing through this axis of rotation. This direction may be “radially inner” or “radially outer” depending on whether it is directed towards the axis of rotation or towards the outside of the tire.
“Elasticity modulus” of a rubber mix is understood to mean a secant modulus of extension at 10% deformation and at ambient temperature.
As far as the metal cords or metal cables are concerned, the measurements of breaking load (maximum load in N), tensile strength (in MPa) and elongation at break (total elongation in %) are carried out under tension in accordance with Standard ISO 6892 of 1984.
As far as the rubber compositions are concerned, the measurements of modulus are carried out under tension in accordance with Standard AFNOR-NFT-46002 of September 1988: the nominal secant modulus (or apparent stress, in MPa) at 10% elongation is measured in a second elongation (i.e. after an accommodation cycle) (normal conditions of temperature and relative humidity in accordance with Standard AFNOR-NFT-40101 of December 1979).
As far as the textile cords or textile cables are concerned, the mechanical properties are measured on fibers which have been subjected to prior conditioning. “Prior conditioning” is understood to mean storage of the fibers for at least 24 hours, before measurement, in a standard atmosphere in accordance with European Standard DIN EN 20139 (temperature of 20±2° C.; relative humidity of 65±2%). The mechanical properties in extension (tenacity, modulus, elongation and energy at break) are measured in known manner using a ZWICK GmbH & Co (Germany) 1435-type or 1445-type tension machine. The fibers, after having received a slight prior protective twist (helix angle of approximately 6°), are subjected to traction over an initial length of 400 mm at a nominal speed of 200 mm/min. All the results are an average of 10 measurements.
U.S. Pat. No. 4,832,102 describes an aircraft tire comprising a crown, two sidewalls and two beads, a carcass reinforcement and a crown reinforcement in which the carcass reinforcement comprises two circumferential alignments of reinforcing threads of high elasticity modulus, anchored in the two beads, and the crown reinforcement comprises at least one working block with at least one ply of reinforcing threads of high elasticity modulus. The carcass reinforcement is anchored in the beads by turning up, around a bead wire, the two circumferential alignments of first reinforcing threads of high elasticity modulus.